Macroinvertebrate community modulates the influence of land use change to the functioning of tropical soils
Globally, harvested areas for bioenergy crops increased 30 million ha between 2005-2010, yielding a total area of 896 million ha dedicated to large-scale biofuel feedstock cultivation by the end of 2010. In Brazil, the additional amount of sugarcane land necessary to meet the demand for ethanol fuel for 2021 is projected to be larger than the total area of countries such as Netherlands or Switzerland. There is a major concern that this expansion of large-scale commercial production of bioenergy feedstock could further intensify the ongoing loss of biodiversity. Land use change (LUC) is the key driver of losses of soil biodiversity and its associated ecosystem functions due to bioenergy crop expansion. A survey was carried out on soil macrofaunal community responses to sugarcane expansion from pasturelands in Brazil and its correlations with soil structural stability, carbon storage and phosphorus availability for plants. We sampled three field sites to represent the Brazilian sugarcane-expansion region. In each field site we identified one chronosequence of land use comprising native vegetation (NV), pasture (PA), and sugarcane (SC).
Macrofauna mean density showed nonsignificant increases from NV to PA but decreased significantly from PA to SC in all sites. An average reduction of 89% in the density of the soil macrofaunal community was observed when sugarcane replaces pasture (or a reduction of 74% compared to NV), and a loss of 39% in the diversity of macrofauna groups (total loss of 53% compared to NV). The overall Shannon’s diversity index dropped from 1.6 under NV to 1.0 under PA, and to 0.7 in SC soils. We showed that while the total soil phosphorus content was not correlated to macrofauna variables, the microbe- and plant-available P pool was strongly correlated to the functional diversity of the soil macrofaunal community. The soil biodiversity loss was also strongly correlated with the observed destabilization of soil structure and ensuing reductions in soil carbon stock across LUC. Our findings consistently indicated that, over a range of soil textures (16 – 66% clay), the abundance of detritivore soil animals, especially earthworms and termites, may be a significant predictor of soil structure transformations due to LUC in tropical environments. Thus, macroinvertebrate community modulates the influence of LUC to the functioning of tropical soils, and monitoring soil macrofaunal community even at a low taxonomic resolution provides a means to also monitor for the functioning of soils across LUC.